The present invention relates to 2,5-dimercapto-1,3,4-thiadiazole reaction products and adducts useful as extreme pressure additives, and more particularly to 2,5-dimercapto-1,3,4-thiadiazole/glycol reaction products and adducts useful as extreme pressure additives.
A variety of additives are used in lubricants to substantially improve performance. For example, extreme pressure additives are routinely incorporated into an untreated (i.e., base) lubricating composition (e.g., grease) to significantly improve performance. Extreme pressure additives are believed to produce a film on the surface of a metal which can both increase the load carrying capacity of lubricant, and protects the metal surface under high load conditions from deterioration due to wear, welding, and abrasion.
Lead naphthenates and lead -dialkyldithiocarbamates are frequently used as additives to improve the EP performance of greases. However, lead is a heavy metal which is considered xe2x80x9cpoisonousxe2x80x9d in all forms. As an alternative, metal additives (such as antimony, zinc, and bismuth) have been used as a replacement for lead. However, these heavy metals still provide environmental concerns regarding the use. Accordingly, it has long been a goal in the art to develop non-metal lubricating materials to replace heavy metal additives while providing acceptable extreme pressure performance.
The effectiveness of potential extreme pressure additives is conventionally ascertained by the 4-Ball Weld Test (ASTM D-2596) and the Timken Load Test (ASTM D-2509). An ideal candidate compound should exhibit good results in both tests since each test quantitates different extreme pressure properties.
Known to those skilled in the art 2,5-dimercapto-1,3,4-thiadiazole (DMTD) derivatives are effective as anti-wear additives in lubricants. Examples of DMTD derivatives useful as anti-wear additives include the monosulfide and disulfide dimers of DMTD as disclosed in U.S. Pat. Nos. 4,517,103 and 5,194,621, maleate adducts of DMTD as disclosed in U.S. Pat. Nos. 5,102,568, 5,055,584 and 5,138,065 and mono-alkylated and thioacteal derivatives as disclosed in U.S. Pat. No. 5,849,925.
DMTD derivatives are also known to provide good 4-Ball Weld properties. In fact, the 4-Ball Weld properties of DMTD derivatives often exceed commercial requirements. Unfortunately, these same derivatives generally exhibit poor Timken Load performance since the DMTD derivatives do not generally provide Timken Loads levels greater than 35 pounds. As a result, commercialization of DMTD derivatives as extreme pressure additives has been limited.
In view of the above, there exists a need in the art for DMTD derivative that provide both adequate 4-Ball Weld and Timken Load properties. Accordingly, it is an object of the present invention to provide DMTD derivatives that provide adequate 4-Ball Weld and Timnken Load properties, which will allow for the effective utilization of DMTD derivatives as extreme pressure additives.
The present invention provides 2,5-dimercapto-1,3,4-thiadiazole/glycol reaction products and adducts useful as extreme pressure additives. In one embodiment, an additive is provided including a reaction product of:
(A) a thiadiazole compound having formula (I): 
where Z is a branched or straight chain C1 to C20 alkyl radical, a C1 to C20 thioalkyl radical, an alpha bound succinate half or full ester, where the ester alkyl is a C1 to C5 alkyl radical, an alkali metal, an alkyloxy linkage having formula (II): 
or combinations thereof, where R1 is hydrogen, a C1 to C20 branched or straight chain alkyl radical, a phenyl radical, a C1 to C20 branched or straight chain alkyl-substituted-phenyl radical, or combinations thereof and R2 is hydrogen, a C1 to C20 branched or straight chain alkyl radical, a phenyl radical, a C1 to C20 branched or straight chain alkyl-substituted-phenyl radical, or combinations thereof; and
(B) a poly(ether)glycol having formula (III): 
where Q is a hydroxyl radical, a branched or straight chain C1 to C20 alkoxy radical, a branched or straight chain C1 to C20 alkoxycarboxyl radical, a mono-substituted, di-substituted, or tri-substituted glycerol residue, hydrogen, or combination thereof; where R3 and R5 are hydrogen, or a methyl radical; where R4 is hydrogen, a branched or straight-chain a C1 to C20 alkyl radical, a phenyl radical, a C1 to C8 branched or straight chain alkyl-substituted-phenyl radical, a C1 to C20 branched or straight chain acyl radical, or combinations thereof; and where n is 1 to 300.
In another embodiment, the present invention provides an additive including a thiadiazole-glycol adduct having formula (IV): 
where R1 is hydrogen, a branched or straight chain C1 to C20 alkyl radical, a phenyl radical, a branched or straight chain C1 to C20 alkyl-substituted-phenyl radical or combination thereof; where R3 is hydrogen, a methyl radical, or combinations thereof, where R4 is hydrogen, a C1 to C20 branched or straight chain alkyl radical, a phenyl radical, a branched or straight chain C1 to C20 alkyl-substituted-phenyl radical, a branched or straight chain C1 to C20 acyl radical, or combinations thereof, and where m is from 1 to 50.
Lubricating compositions including the reaction products and adducts of the present invention are also provided. Advantageously, the lubricating compositions of the invention exhibit significantly improved Timken load properties as compared previous DMTD derivatives. These and other advantages of the present invention will be readily apparent from the detailed description set forth below.
Present invention provides reaction products and adducts of mono-substituted-2,5-dimercapto-1,3,4-thiadiazole derivatives (hereinafter xe2x80x9cthiadiazole compoundsxe2x80x9d) and poly(ether)glycols useful as extreme pressure additives in lubricants. The thiadiazole-glycol reaction products and adducts have unexpectedly been found to provide good Timken Load properties in addition to good 4-Ball Weld properties. Advantageously, the reaction products and adducts provide an alternative to the heavy metal extreme pressure additives commonly used in lubricants.
In one embodiment the present invention provides an additive including a reaction product of a thiadiazole compound and a poly(ether)glycol. The thiadiazole compound is a mono-substituted 2,5-dimercapto-1,3,4-thiadiazole having formula (I): 
in which the substituent xe2x80x9cZxe2x80x9d is either: (1) a branched or straight chain C1 to C20 alkyl radical, with C1 to C8 radical being preferred; (2) a branched or straight chain C1 to C20 thioalkyl radical with a C1 to C8 radical being preferred; (3) an alpha bound succinate half or full ester, where the ester alkyl is a C1 to C5 alkyl radical; (4) an alkyloxy linkage having formula (II) 
(5) an alkali metal; or a combination thereof. In this context, xe2x80x9calpha boundxe2x80x9d means that the thiadiazole moiety is bound to a carbon atom in an alpha position relative to the carbonyl moiety of the full or partial ester. When Z is an alkyloxy linkage the substituent R1 is either: (1) hydrogen; (2) a branched or straight chain C1 to C20 alkyl radical, with a C1 to C8 alkyl radical being preferred; (3) a phenyl radical; (4) a branched or straight chain C1 to C20 alkyl-substituted-phenyl radical, with a C1 to C8 alkyl substituent being preferred; or a combination thereof. Likewise, the substituents for R2 are independently chosen from the same group of substituents described for R1. In a preferred embodiment, when Z is an alkyloxy linkage R1 is hydrogen and R2 is a C3 to C8 alkyl radical.
Thiadiazole compounds falling within the above-described parameter are known in the art and are easily synthesized following known techniques. For example, thiadiazole compounds having an alpha bound succinate half or full ester are disclosed in U.S. Pat. No. 5,055,584, which is incorporated herein by reference.
The second component for synthesizing the thiadiazole-glycol reaction product is a poly(ether)glycol having formula (III): 
in which Q is either: (1) a hydroxy radical; (2) a branched or straight chain C1 to C20 alkoxy radical, with a C1 to C10 radical being preferred; (3) a branched or straight chain C1 to C20 alkoxycarboxyl radical, with a C1 to C10 radical being preferred; (4) a mono-substituted, di-substituted, or tri-substituted glycerol residue; (5) hydrogen; or a combination thereof. The substituents R3 and R5 are either: hydrogen; or a methyl radical. The substituent R4 is either: (1) hydrogen; (2) a branched or straight chain C1 to C20 alkyl radical, with a C1 to C8 radical being preferred; (3) a phenyl radical; (4) a branched or straight chain C1 to C20 alkyl-substituted-phenyl radical, with a C1 to C8 alkyl substituent being preferred; (5) a branched or straight chain C1 to C20 acyl radical, with a C1 to C10 radical being preferred; or a combination thereof. The number of ether repeating units xe2x80x9cnxe2x80x9d ranges from 1 to 300, with 1 to 150 being preferred, with 1 to 10 being more preferred.
Poly(ether)glycols falling within the above described parameters are known in the art. Representative examples of the glycols include, but are not limited to, polyethylene glycol, polypropylene glycol, tetraethylene glycol, ethyloxytriethyleneglycol, butoxytriethylene glycol, dimethoxytriethyleneglycol, triethyleneglycol di-nonanoate, butoxytriglycol, and triethyleneglycol dimethylether. One particularly preferred glycol is butoxytriethylene glycol. The glycols are commercial available from a variety of sources. Preferably, the glycols have a molecular weight from 340 to 4000, with 340 to 1000 being preferred. The glycols should have a viscosity less than 4000 centistokes at 25xc2x0 C. for ease of handling. Likewise, the glycols should have a minimal effect on the dropping point of greases.
The reaction product is formed by combining the two sole components with or without a solvent and subsequently heating the components, if necessary. Preferably, the thiadiazole compound is dispersed in the glycol, which is normally in a liquid state at room temperature. Heating the thiadiazole/glycol mixture is not required when the thiadiazole compound is in a liquid state at room temperature. However, if the thiadiazole compound is in a solid state at room temperature, the mixture may be heated (e.g., to at least 100xc2x0 C.) to facilitate formation of the reaction product. The requisite temperature and time needed to facilitate formation of the reaction product is variable and can easily be determined by one skilled in the art. The formation of the reaction produced can approximated by observing the dissolution of the thiadiazole compound, which is normally solid at room temperature. The formation of the reaction product can also be confirmed by Infrared Spectroscopy (IR) since shifts in absorption are observed when comparing the IR spectra for the individual components versus the IR spectra for the reaction product.
The thiadiazole compound and the poly(ether)glycol are preferable reacted in a
molar ratio or the starting materials of at least 0.2:1, with a ratio of at least 0.4:1 being more preferred. However, for further improved extreme pressure properties an equimolar or an excess ratio of the thiadiazole compound can be used (e.g., a molar ratio of 1:1, 2:1 or greater).
In another embodiment the present invention provides an additive including a mon-substituted thiadiazole-glycol condensation adduct having formula (IV): 
in which R1, R3, R5 and R4 are independently selected from the above-described group of substituents for the reaction products. The number of repeating ether units xe2x80x9cmxe2x80x9d in the glycol moiety is 1 to 50, with 1 to 10 being preferred, and 1 to 3 being more preferred.
The thiadiazole-glycol adduct is prepared by reacting in a 1:1:1 molar ratio 2,5-dimercapto-1,3,4-thiadiazole (DMTD) with an aldehyde containing the substituent R1 and a poly(ether)glycol as previously described for the reaction products. The components are mixed and heated for a sufficient amount of time to form the condensation adduct. Examples of the synthesis of similar condensation adducts with monohydric alcohols instead of glycols are disclosed in U.S. Pat. No. 5,194,621, which is incorporated herein by reference. These parameters can be easily modified by one skilled in the art.
The thiadiazole reaction products and adducts are incorporated as additives into lubricating compositions in an effective amount to impart adequate extreme pressure properties. In this context, adequate extreme pressure properties are considered to be passing a Timken Load of at least 40 pounds, with at least 50 pounds or greater being preferred. As will be apparent to one skilled in the art, the amount of the reaction products and adducts needed to provide adequate extreme pressure properties is variable. The additives can be added in a range from 0.1 to 10 weight percent of the lubricating composition, with at least 1 weight percent being preferred and at least 2 weight percent being more preferred.
In accordance with the present invention lubricating compositions suitable for incorporation of the extreme pressure additives include, but are not limited to, lubricating oils, engine oils and lubricating greases containing a major amount of base oil. A xe2x80x9cmajor amountxe2x80x9d in this context means that greater than 50 weight percent (wt. %) of the composition is base oil. Base oils to be used include, but are not limited to, napthenic, aromatic, parafinic, mineral, and synthetic oils. Representative synthetic oils include, but are not limited to, polysiloxanes, carboxylic acid esters and polyglycol ethers.
In a preferred embodiment, the lubricating composition is a grease which is prepared by adding to a base oil thickeners such as salts and complexes of fatty acid soaps, polyurea compounds, mixed and complex soaps of alkali metals, alkaline earth metals, aluminum, modified clays and quaternary ammonium bentonite complexes. Various other additives can be incorporated as desired.